Bạn tham khảo:
$2\div\dfrac{2}{3}-\dfrac{1}{7}$
$=2\times\dfrac{3}{2}-\dfrac{1}{7}$
$= \dfrac{6}{2} - \dfrac{1}{7}$
$= 3 -\dfrac{1}{7}$
$=\dfrac{21}{7}-\dfrac{1}{7}$
$=\dfrac{20}{7}$
$\dfrac{2}{3}+\dfrac{5}{2}-3$
$=\dfrac{4}{6}+\dfrac{15}{6}-3$
$=\dfrac{19}{6}-3$
$=\dfrac{19}{6}-\dfrac{18}{6}$
$=\dfrac{1}{6}$